Amplitude Modulation Detection by Listeners with Unilateral Dead Regions

Background: A dead region is a region in the cochlea where the inner hair cells and/or neurons are functioning very poorly, if at all. We have shown that, for people with sensorineural hearing loss, thresholds for detecting sinusoidal amplitude modulation (AM) of a sinusoidal carrier were lower for ears with high-frequency dead regions, as diagnosed using the threshold-equalizing noise test, calibrated in hearing level, than for ears without dead regions when the carrier frequency was below the edge frequency, fe, of the dead region. Purpose: To measure AM-detection thresholds for subjects with unilateral dead regions, using carrier frequencies both below and above fe. Research Design: Ten subjects with bilateral high-frequency hearing loss, but with unilateral high-frequency dead regions, were tested. The carriers were presented at sensation levels of 5, 10, or 15 dB. The values of fe were close to 1000, 1500, or 2000 Hz. Results: For carrier frequencies below fe, AM-detection thresholds were lower for the ears with dead regions than for the ears without dead regions, replicating earlier findings. In contrast, for carrier frequencies above fe, AM-detection thresholds tended to be higher for ears with dead regions than for ears without dead regions. Conclusions: The reason why AM detection was poorer in the ears with dead regions for carrier frequencies above fe is unclear. However, this finding is consistent with the generally poor discrimination of sounds that has been reported previously for sounds with frequency components falling within a dead region. The results have implications for the ability of people with dead regions to use information from frequency components falling inside the dead region.